1. Field of the Invention
The present invention relates to a method and an apparatus for determining a slip value that describes the torque transmission reliability between two conical disk pairs of a belt-driven conical-pulley transmission that are frictionally engaged by an endless torque-transmitting means.
2. Description of the Related Art
For reasons of convenience, fuel consumption, and the environment, automated power trains are being used increasingly in motor vehicles. Such power trains contain, for example, a belt-driven conical-pulley transmission having a continuously variable transmission ratio. For continuously reliable operation of such a transmission, suitable contact pressure between the endless torque-transmitting means and the conical disks is important. Suitable signifies first that the contact pressure ensures that the endless torque-transmitting means does not slip, and second that the contact pressure is not unnecessarily high, so that it does not produce any unacceptable loads on parts and detract from the efficiency as a result of the high hydraulic pressure that must be provided. To control or regulate the contact pressure efficiently, precise knowledge of the reliability of torque transmission, or of the slippage condition, between the conical disks of the belt-driven conical-pulley transmission and the endless torque-transmitting means is necessary. Direct measurement of that slippage is complicated and expensive, since in addition to the rotational speeds of the pairs of conical disks and the speed of the endless torque-transmitting means, it is also necessary to know the exact effective radii at which the frictional engagement between the endless torque-transmitting means and the conical surfaces of the pairs of conical disks occurs.
If a slip value corresponding to the torque transmission capability of the belt-driven transmission or the latter's slippage condition is determined by modulating the contact pressure of the conical disks and determining the slip value for example by a lock-in principle or a fast Fourier transformation (FFT transformation), possibly using band pass filtering, that generally does not lead to well defined results.
An object of the present invention is to provide a method and/or an apparatus of the type described at the beginning, with which a slip value can be determined that gives the most meaningful information possible about the torque transmission reliability of the belt-driven transmission.